Automotive air conditioning systems employ a compressor that is driven by the engine through an electromagnetic clutch. In practice, it is common to provide some form of clutch switching and pressure relief to protect the system from extreme high pressure. For example, it is desirable that the compressor not operate above a certain high pressure (for example, 550 psig), since pressures above this extreme may adversely affect compressor and/or other components life. It is further desirable that the high pressure relief, normally involving venting to atmosphere, be provided as secondary rather than primary protection against high pressure. Accordingly, various clutch switching and pressure relief arrangements have been proposed to satisfy these requirements. An example of one of the more sophisticated and successful devices for this purpose is disclosed in U.S. Pat. No. 4,400,601 to Brucken assigned to General Motors Corporation.
The device disclosed in the Brucken patent is an integrated unit including an electrically conductive housing adapted to be electrically grounded on mounting in the compressor cylinder head. The device actually includes both low pressure and high pressure switches that are operatively electrically connected in series for adaptation in a control circuit. Under normal or acceptable operating pressures, both the low pressure and high pressure switches are biased to a normally closed position. In the event the pressure falls above or below the normal operating pressure range, either the low pressure or high pressure switch opens so as to open the circuit and disengage the electromagnetic clutch, thereby terminating compressor operation.
The device also includes a high pressure relief valve. This valve is normally biased closed and is responsive to a predetermined extreme high pressure value substantially higher than the pressure value that opens the high pressure relief switch. Consequently, the high pressure relief valve serves as a secondary high pressure protection and operates where for some reason pressure in the system continues to rise after the clutch is disengaged.
While the combination cut-off switch/relief valve device disclosed in the Brucken patent represented a significant advance in the art at the time of its development, further improvement remains a goal. In particular, while the device represented a successful structure at the time of its development, it includes a relatively large number of working parts. As such, a less complicated, simplified structure that is less expensive to manufacture is desired. A more reliable structure presenting a reduced number of potential leak pathways and increased overall operating efficiencies is also sought.